This Competing Continuation Application requests funding for years 06 to 10 of the NIMH collaborative Multimodal Treatment Study of Children with Attention-Deficit Hyperactivity Disorder (MTA Study). In a parallel-group design, 576 rigorously diagnosed children with ADHD (96 at each of 6 sites), age 7-9, are randomly assigned to four treatment conditions:(1 )a Medication-only Treatment; (2) a Psychosocial-only Treatment; (3) a Combined (medication & psychosocial) Treatment; or (4) an Assessment-and Referral-only condition. All but the latter are treated intensively for 14 months, with assessments for all subjects at baseline, 3, 9, 14, and 24 months. The original MTA design thus provides short-tenn (10 months post- treatment) follow-up at 24 months, but insufficient funds and time prevented longer-term follow-up. This Continuation request, in concert with the companion Competing Supplement for years 04 and 05, would begin the longer-term follow-up of differential treatment effects by following all subjects at least through heir 5th year (4 yr post- treatment). Continuation Aim 1 is to conduct confirmatory tests of the hypothesis that a Combined Treatment strategy, integrating medication & psychosocial components, is significantly more effective in producing long-term therapeutic gains and preventing new psychopathology than Medication or Psychosocial Treatment alone, and that the difference is clinically meaningful. Continuation Aim 2 is to conduct confirmatory tests of the hypothesis that systematic, intensive treatments (all 3 MTA treatments) significantly more effective (statistically and clinically) in producing long-term therapeutic gains and preventing new psychopathology than treatments typically received in the community. Continuation Aim 3 is to conduct confirmatory tests of the hypothesis that systematic, state-of-the-art treatments for ADHD in early childhood alter the risk for subsequent patterns of substance use and abuse, and that the risk alteration is clinically significant. Continuation Aim 4 is to conduct exploratory analyses to determine whether pre-treatment individual differences (severity, comorbidity, parent functioning, family history) are associated with patterns of stability change in treatment effects. Continuation Aim 5 is to conduct exploratory analyses to determine the extent to which patterns of stability/change in therapeutic attitudes, attributions, philosophies, and treatment-related behaviors vary as a function of randomly assigned treatment, pre-posttreatment differences in functioning, post-treatment reports of satisfaction, and preexisting characteristics.